Transfer case arrangement

ABSTRACT

The invention relates to a transfer case arrangement comprising a first output shaft, a second output shaft, a clutch for the distribution of a torque between the output shafts, a shutdown device for the shutting down of the second output shaft when the clutch is disengaged and a lubrication device for the lubrication of the clutch and/or of another component of the transfer case arrangement.

The invention relates to a transfer case arrangement having a first output shaft, a second output shaft, a clutch for the distribution of a torque between the output shafts and a shutdown device for the shutting down of the second output shaft with a disengaged clutch.

Such a transfer case arrangement is generally known and is used, for example in a motor vehicle, to permanently drive a vehicle axle, e.g. a rear axle, connected to the first output shaft and to additionally transmit, when required, drive torque via the second output shaft to a second vehicle axle, e.g. a front axle. The first vehicle axle permanently driven by the first output shaft is also called the primary axle, whereas the optionally drivable second vehicle axis is called a secondary axle.

The transmission of drive torque via the second output shaft to the secondary axle takes place by an at least partial engagement of the clutch of the transfer case. When the clutch is disengaged, the second output shaft, and consequently also the secondary axle, is, in contrast, not loaded with drive torque. To prevent unnecessary moments of inertia and drag losses from being generated in that the second output shaft is set into rotation by vehicle wheels connected to the secondary axle with a disengaged clutch, it is known to provide a shutdown device by which the second output shaft can be shut down when the clutch is disengaged in that it is decoupled from the vehicle wheels.

Known transfer cases typically—independently of whether they have a shutdown device for the shutting down of the second output shaft or not—have a lubrication device for the lubrication of the clutch and/or of another component, e.g. of a bearing, of the transfer case, said lubrication device having a pump for the conveying of lubrication oil from an oil sump of the transfer case to the clutch and/or to the other component.

Conventionally, the pump is an electrically driven pump or a pump driven by the first output shaft, for example a gerotor pump which continuously conveys lubrication oil.

Such pumps result in a deterioration of the efficiency of the transfer case so that pump-less lubrication devices have been developed which convey lubrication oil from the transmission sump to the clutch and/or bearings of the transfer case while utilizing a chain drive or a gear connection between the output of the clutch and the second output shaft.

If such pump-less lubrication devices are provided in a transfer case arrangement with a shutdown device, the problem, however, occurs that no lubrication oil conveying takes place when the second output shaft is shut down. This impairs the lubrication of the clutch and/or of the bearings of the transfer case and can result in damage to the transfer case at least in the long term.

It is the underlying object of the invention to provide a transfer case arrangement of the initially named kind whose reliable function is permanently ensured.

A transfer case arrangement having the features of claim 1 is provided to satisfy the object.

The transfer case arrangement in accordance with the invention includes a first output shaft, a second output shaft, a clutch for the distribution of a torque between the output shafts, a shutdown device for the shutting down of the second output shaft when the clutch is disengaged and a lubrication device for the lubrication of the clutch and/or of another component, e.g. of a bearing, of the transfer case arrangement, with the lubrication device having an oil conveying device or the conveying of lubrication oil. A control is furthermore provided which serves to activate the oil conveying device from time to time when the second output shaft is shut down.

Since the control provided in accordance with the invention provides an activation of the oil conveying device from time to time when the second output shaft is shut down, it is ensured that a quantity of lubrication oil is conveyed which is sufficient for an ideal lubrication of the clutch and/or of the other transmission component even with a shut down second output shaft, for example with a vehicle drive only via the primary axle. Since an oil conveying is typically anyway provided with a driven second drive shaft, a sufficient lubrication of the clutch or of the other transmission component is therefore always ensured and a prerequisite for a long-term reliable function of the transfer case is thus provided.

Since the control provided in accordance with the invention does not provide a continuous oil conveying with a shut down second output shaft, but only an activation of the oil conveying device from time to time, churning losses accompanying the oil conveying as well as unwanted moments of inertia, which can occur, for example, when the oil conveying is based on a rotation of the second output shaft, are furthermore minimized, which ultimately contributes to a better efficiency of the transfer case arrangement.

Advantageous embodiments of the invention can be seen from the dependent claims, from the description and from the drawing.

In accordance with a first embodiment, the control serves to activate the oil device intermittently, i.e. to repeatedly switch the oil conveying device on and off, with a shut down second output shaft. In this respect, the switching on and off of the oil conveying device can take place at regular or irregular time intervals with the activation or deactivation of the oil conveying device being able to follow a fixedly preset pattern or being able to be carried out in a demand-oriented manner.

The oil conveying device can in particular be activated on a braking of the vehicle, e.g. by an engine brake or by a foot brake, since losses accompanying the actuation of the oil conveying device, for example drag losses and/or moments of inertia, do not have a disadvantageous effect, but rather an advantageous one. In addition, the actuation of the oil conveying device contributes to the heating of the transfer case and/or of an axial differential of the secondary axle, which has an advantageous effect on the efficiency of the transmissions.

The oil conveying device can include an electrically driven pump or a pump driven by the second output shaft, e.g. a gerotor pump. Alternatively, the oil conveying device can be formed by a chain drive or by a gear connection which is connected between an output of the clutch and the second output shaft.

In the case of an electrically driven pump, the activation of the oil conveying device can take place by an activation signal of the control output to the pump directly.

If, in contrast, the oil conveying device is formed by a pump driven by the second output shaft or by a chain drive or a gear connection, the activation of the oil conveying device preferably takes place by an at least partial engagement of the clutch. Some of the drive torque is branched off from the first output shaft to the second output shaft by the at least partial engagement of the clutch, whereby the second output shaft is set into rotation and the oil conveying device is set into motion. The second output shaft shut down per se is in other words therefore temporarily set into rotation for the oil conveying.

In particular in the case that the oil conveying device is formed by a pump driven by the second output shaft or by a chain drive or a gear connection, it proves to be particularly advantageous if the control is made to activate the oil conveying device during a deceleration or a coasting mode of a motor vehicle in which the transfer case arrangement is arranged since the acceleration of the previously shut down second output shaft can be carried out with particular fuel economy in this manner and ultimately better fuel efficiency is achieved.

The oil conveying device is preferably made so that it conveys the lubrication oil from an oil sump of the transfer case into a region of the transfer case disposed above the clutch or above the other component.

Furthermore, the lubrication device can include an oil reservoir for the collection of lubrication oil conveyed by the oil conveying device, in particular such that an oil level in the oil reservoir is above an outlet opening of a supply line leading from the oil reservoir to the clutch or to the other component. Such an oil reservoir so-to-say acts as a buffer or intermediate store which ensures that sufficient lubrication oil is also available for the lubrication of the clutch or of the other transmission component between two oil conveying procedures. The position of the oil level in the oil reservoir above the outlet opening of the supply line makes it possible that the oil can only flow out of the oil reservoir to the clutch or to the other transmission component due to gravity, i.e. without any additional pumping effect.

The length of an oil conveying procedure and the time interval between two sequential oil conveying procedures are preferably matched to the oil reservoir and/or to the supply line such that an oil level sufficiently high for a reliable lubrication is always ensured in the oil reservoir. Alternatively or additionally, the oil reservoir can have an oil level sensor which detects the level of the oil in the oil reservoir and transmits a corresponding signal to the control when the oil level falls below a critical lower limit and an activation of the oil conveying device is required.

In accordance with a further embodiment, the second output shaft serves for the transmission of drive torque to wheels of a motor vehicle and the shutdown device is connected between the wheels and the second output shaft. The second output shaft can therefore be decoupled from the wheels by the shutdown device to prevent the second output shaft from being set into rotation by the wheels with a disengaged clutch of the transfer case.

The shutdown device can in this respect be arranged directly at the hubs of the wheels. This has the advantage that not only the second output shaft, but rather also the vehicle axle connected thereto and driving the wheels, i.e. the secondary axle, can be decoupled with respect to a rotation of the wheels. The shutdown device therefore thus effects a shutdown not only of the second output shaft, but also of the secondary axle. With a shutdown device arranged at the hubs of the wheels, it can be a question of dog clutches which can e.g. be actuated by negative pressure, for example from a vacuum pump for a brake power assist unit or from an intake restriction of the throttle, or also electromagnetically.

Alternatively, the shutdown device can be arranged at an axial differential, in particular at an output or at both outputs of the axial differential, of a vehicle axle driving the wheels, in other words that is of the secondary axle. In this case, the shutdown device is therefore connected between the secondary axle and the second output shaft so that only the second output shaft can be shut down, whereas the secondary axle is set into rotation by the wheels with a moving vehicle. A shutdown device of this kind can, for example, be a friction clutch actuated by an electric motor or one or two dog clutch(es).

A further subject of the invention is also a method for the lubrication of a clutch and/or of another component of a transfer case arrangement having the features of claim 11. The aforesaid advantages can be achieved accordingly by the method in accordance with the invention. Advantageous embodiments of the method result from the embodiments of the transfer case arrangement in accordance with the invention described above.

The invention will be described in the following purely by way of example with reference to an advantageous embodiment and to the enclosed drawing.

FIG. 1 shows a schematic representation of a transfer case arrangement in accordance with the invention.

A transfer case arrangement of a motor vehicle which has an engine 10 and a transfer case 12 is shown in FIG. 1. The transfer case 12 includes a drive shaft 14 which is driven by the engine 10 and which is rigidly connected to a first output shaft 16 of the transfer case 12. The combination of drive shaft 14 and first output shaft 16 is also called a main shaft. The transfer case 12 can furthermore optionally have a step-down transmission (not shown) arranged at the first drive shaft 14 for the switching in of an off-road gear (hi/lo gear).

The first output shaft 16 is connected via an axial differential 18 to a first vehicle axle 20. The first vehicle axle 20 is driven permanently by the first output shaft 16 so that the first vehicle axle 20 is also called the primary axle. The primary axle 20 serves for the driving of vehicle wheels 22.

The transfer case 12 furthermore has a second output shaft 24 which is connected via an axial differential 26 to a second vehicle axis 28, the so-called secondary axle, which serves for the driving of vehicle wheels 30.

In the present embodiment, the primary axle 20 represents a rear axle of the vehicle and the vehicle wheels 22 correspondingly represent rear wheels, while the secondary axle 28 is a front axle and the vehicle wheels 30 are front wheels of the vehicle. Generally, however, the primary axle 20 can also be a front axle and the secondary axle 28 can be a rear axle.

For the distribution of the drive torque of the engine 10 between the first output shaft 16 and the second output shaft 24, the transfer case 12 has a clutch 32 which is connected at the input side to the first output shaft 16 and at the output side to the second output shaft 24. The clutch 32 is a friction clutch, for example a multi-disk clutch, and in particular a wet multi-disk clutch

The actuation of the clutch 32, i.e. that is the engagement state or disengagement state of the clutch 32, is controlled by means of a control 34. The proportion of the drive torque which is or can be transmitted via the second output shaft 24 to the front wheels 30 is set by the degree of the engagement of the clutch 32.

A chain drive 36 is connected between the output side of the clutch 32 and the second output shaft 24, with a gear connection also being able to be provided instead of a chain drive 36. The chain drive 36 does not only serve for the transmission of torque from the clutch 32 to the second output shaft 24, but rather it additionally conveys lubrication oil from an oil sump 38 arranged in a lower region of the transfer case 12 into a region of the transfer case 12 disposed above the clutch 32. The chain drive 36 therefore forms an oil conveying device 40 in addition to a torque transmission device.

The lubrication oil conveyed upward by the chain drive 36 serves for the lubrication of the clutch 32 as well as of other components of the transfer case 12, such as of bearings, and is collected in an oil reservoir 42. The lubrication oil conveyed upward is stored in the oil reservoir 42 such that the oil level in the oil reservoir 42 is above an outlet opening of a supply line (not shown) leading from the oil reservoir 42 to the clutch 32 or to the other components of the transfer case 12 so that the lubrication oil can flow to the clutch 32 or to the other transmission components due to gravity.

It must be pointed out that the oil reservoir 42 does not necessarily have to be provided. Instead, it is also possible to supply the lubrication oil conveyed upward by the chain drive 36 directly to the clutch 32 or to the other components of the transfer case 12.

It is easy to understand that the chain drive 36 only acts as an oil conveying device 40 when the second output shaft 24 rotates, i.e. that is when the clutch 32 is at least partially engaged, and/or when the second output shaft 24 is driven by the front wheels 30 with a moving vehicle. Conversely, no oil conveying takes place when the second output shaft 24 is stationary.

To prevent the secondary axle 28 and the second output shaft 24 from being set into motion by the rotating front wheels 30 with a disengaged clutch 32, i.e. on a drive of the vehicle exclusively via the primary axle 20, and thus from unnecessary moments of inertia being produced, a shutdown device is provided for the shutting down of the secondary axle 28 and of the second output shaft 24. The shutdown device is formed by dog clutches 44 arranged at the hubs of the front wheels 30 by which the front wheels 30 can be rotationally effectively decoupled from the secondary axle 28.

Alternatively, the shutdown device can also be arranged at the axial differential 26 of the secondary axle 28. In this case, only the second output shaft 24 would be rotationally effectively decoupled from the front wheels 30, whereas the secondary axles 28 would always rotate together with the front wheels 30.

It has already been mentioned that no conveying of lubrication oil from the oil sump 38 into the oil reservoir 42 takes place when the secondary output shaft 24 is shut down. On a drive of the vehicle only via the primary axle 20, there is therefore generally the danger that sufficient lubrication oil is not available in the oil reservoir 42 for the lubrication of the clutch 32 or of the other transmission components.

In order always to store a quantity of lubrication oil in the oil reservoir 42 sufficient for the lubrication of the clutch 32 and of the other transmission components or in order also to ensure a sufficient lubrication of the clutch 32 and of the other transmission components without any oil reservoir 42 present, the control 34 therefore ensures that an oil conveying also takes place from time to time with a generally shut down second output shaft 24 in that the control 34 commands an at least partial engagement of the clutch 32 from time to time, whereby the chain drive 35 is actuated and an oil conveying is thus set in motion.

In this respect, the engagement of the clutch 32 from time to time, and thus the length of an oil conveying procedure or the time interval between two sequential oil conveying procedures, can follow a predetermined regular or irregular pattern or can take place in a demand-oriented manner with reference to the oil level in the oil reservoir 42 which can be detected with the help of a suitable oil level sensor or determined with reference to a map or calculation model and transmitted to the control 34. In addition, the clutch 32 can always be engaged when the vehicle is braked, e.g. by a foot brake or by an engine brake.

Finally, it must be pointed out that the oil conveying device 40 for the conveying of lubrication oil from the oil sump 38 into the oil reservoir 42 does not necessarily have to be a chain drive 36 or a corresponding gear connection connected between the clutch 32 and the second output shaft 24, but that the oil conveying device 40 can rather also be a separate oil pump. Such an oil pump can, for example, be a gerotor pump which is driven by the second output shaft 24 and which is actuable by an at least partial engagement of the clutch 32 from time to time with a generally shut down second output shaft 24 in accordance with the chain drive 36. Alternatively, the oil pump can, however, also be an electrically driven pump which is activated occasionally by the control 34 or by another suitable control when the output shaft 24 is shut down.

Reference numeral list 10 engine 12 transfer case 14 drive shaft 16 first output shaft 18 axial differential 20 first vehicle axle/primary axle 22 vehicle wheels 24 second output shaft 26 axial differential 28 second vehicle axle/secondary axle 30 vehicle wheels 32 clutch 34 control 36 chain drive 38 oil sump 40 oil conveying device 42 oil reservoir 44 dog clutch 

1. A transfer case arrangement comprising a first output shaft; a second output shaft; a clutch for distributing a torque between the output shafts; a shutdown device for shutting down the second output shaft when the clutch is disengaged; a lubrication device for lubricating the clutch and/or another component of the transfer case arrangement, the lubrication device having an oil conveying device for conveying lubrication oil; and a control that activates the oil conveying device periodically when the second output shafts shut down.
 2. The transfer case arrangement in accordance with claim 1, wherein the control activates the oil conveying device intermittently when the second output shaft is shut down.
 3. The transfer case arrangement in accordance with claim 1, wherein the oil conveying device includes an electrically driven pump or a pump driven by the second output shaft.
 4. The transfer case arrangement in accordance with claim 1, wherein the oil conveying device is formed by a chain drive or by a gear connection connected between an output of the clutch and the second output shaft.
 5. The transfer case arrangement in accordance with claim 1, wherein activation of the oil conveying device takes place by an at least partial engagement of the clutch.
 6. The transfer case arrangement in accordance with claim 1, wherein the oil conveying device conveys the lubrication oil from an oil sump of the transfer case into a region of the transfer case disposed above the clutch or above the another component.
 7. The transfer case arrangement in accordance with claim 1, wherein the lubrication device includes an oil reservoir for collecting the lubrication oil conveyed by the oil conveying device such that an oil level in the oil reservoir is above an outlet opening of a supply line leading from the oil reservoir to the clutch or to the another component.
 8. The transfer case arrangement in accordance with claim 1, wherein the second output shaft transmits of torque to wheels of a motor vehicle and the shutdown device is connected between the wheels and the second output shaft.
 9. The transfer case arrangement in accordance with claim 1, wherein the shutdown device is arranged at the hubs of the wheels.
 10. The transfer case arrangement in accordance with claim 1, wherein the shutdown device is arranged at an output of an axial differential of a vehicle axle driving the wheels.
 11. The transfer case arrangement in accordance with claim 1, wherein the control activates the oil conveying device during a deceleration or a coasting mode of a motor vehicle in which the transfer case arrangement is arranged.
 12. A method for lubricating a clutch and/or another component of a transfer case arrangement that includes a first output shaft and a second output shaft, the clutch distributing a torque between the output shafts the method comprising: shutting down the second output shaft with a shutdown device when the clutch is disengaged; and lubricating the clutch and/or the another component of the transfer case arrangement with a lubrication device having an oil conveying device for conveying lubrication oil, the oil conveying device being activated periodically when the second output shaft is shut down.
 13. The method in accordance with claim 12, wherein the oil conveying device is activated by an at least partial engagement of the clutch.
 14. The method in accordance with claim 12, wherein the oil conveying device is activated during a deceleration or a coasting mode of a vehicle in which the transfer case arrangement is arranged. 